**Question:** Influenza pandemic is mainly caused by-

A. Avian influenza
B. Human-to-human transmission
C. Pig influenza
D. Oceanic influenza

**Correct Answer:** A. Avian influenza

**Core Concept:** Influenza pandemics occur when a new strain of the influenza virus emerges, causing widespread infections in humans. The term "avian influenza" refers to the type of influenza that primarily affects birds, but can occasionally infect humans, leading to potential pandemics.

**Why the Correct Answer is Right:** Avian influenza, caused by the H5N1, H7N9, or other subtypes of the virus, is responsible for influenza pandemics. These strains originate from birds, particularly infected poultry, and can be transmitted to humans through direct contact or consumption of contaminated food. In rare cases, human-to-human transmission can occur, but this is not the primary mode of infection.

**Why Each Wrong Option is Incorrect:**

B. Human-to-human transmission: The pandemic primarily occurs when a new strain emerges, not through direct human-to-human transmission.

C. Pig influenza: Swine influenza (H1N1) is a different subtype and does not explain avian influenza pandemics.

D. Oceanic influenza: This option is unrelated to the cause of influenza pandemics and refers to ocean-borne diseases, which is not relevant to the topic at hand.

**Why the Correct Answer is Right:** Avian influenza is caused by the transmission of the virus from birds to humans, resulting in a new strain that can infect a larger population. This can lead to pandemics due to the unfamiliarity of the virus among humans, causing widespread illness and potentially high mortality rates.

**Clinical Pearl:** To prevent avian influenza pandemics, maintaining biosecurity measures in poultry farms, regular vaccination of humans, and public health measures like surveillance and containment are essential. Additionally, cooking poultry thoroughly can help prevent the transmission of the virus from birds to humans.